Weight sensor assembly for determining seat occupant weight

ABSTRACT

A system for measuring the weight of a seat occupant is used to control airbag deployment. The system includes a plurality of weight sensors that have a first end mounted to a seat riser and a second end mounted to a seat frame or track member. The weight sensors have a central bendable portion that extends between the first and second ends. A groove is formed in one of the external surfaces of the central bendable portion to localize strain. A full bridge strain gage assembly is mounted on a surface of each of the weight sensors, opposite from the groove, for generating a weight signal in response to measuring deflection of the central bendable portion. A central processor determines seat occupant weight based on the weight signals and an airbag control module communicates with the processor. The control module controls deployment force of the airbag based on seat occupant weight.

RELATED APPLICATION

[0001] This application claims priority to provisional application60/141,105 filed on Jun. 25, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to an apparatus for measuring the weightof a seat occupant. Specifically, a sensor arrangement is mounted to aseat frame member to provide seat occupant weight measurements.

[0004] 2. Related Art

[0005] Most vehicles include airbags and seatbelt restraint systems thatwork together to protect the driver and passengers from experiencingserious injuries due to a high speed collision. It is important tocontrol the deployment force of the airbags and the force of theseatbelt pre-tensioners based on the size of the driver or thepassenger. One way to control these forces is to monitor the weight ofthe seat occupant. If a smaller person such as a child or infant in acar seat is in the front passenger seat, the weight on the seat will beless than if an adult occupies the seat.

[0006] Current systems for measuring the weight of a seat occupant arecomplex and expensive. One type of system uses pressure sensitive foilmats mounted within the seat bottom foam. Another system uses sensorsplaced at a plurality of locations within the seat bottom cushion. Thecombined output from the mats or the sensors is used to determine theweight of the seat occupant. These sensors experience a substantiallyvertical force, due to the weight of the seat occupant, but are alsosubject to longitudinal and lateral forces caused by acceleration,deceleration, or turning. The lateral and longitudinal forces picked upby the sensor incorporate an error component into the weightmeasurement. The sensors are very sophisticated using multiple straingages and complicated bending elements to provide high measurementsensitivity in the vertical direction and low sensitivity to lateral andlongitudinal forces in order to increase accuracy.

[0007] Mounting these sensors within the seat bottom can also bedifficult and time consuming. It is difficult to find mounting locationsfor each the sensors that will accommodate all of the various positionsof a seated occupant while still providing accurate measurements.Further, shifting of the occupant on the seat can dislodge or move thesensors out of their proper location. Because the sensors are mountedwithin the seat bottom, it is difficult to reposition the sensors afterthe seat is installed in the vehicle.

[0008] Thus, it is desirable to have a simplified seat occupant weightmeasurement system that is accurate and easily to install and overcomesthe above references deficiencies with prior art systems.

SUMMARY OF THE INVENTION

[0009] In a disclosed embodiment of this invention, a system formeasuring the weight of an occupant seated on a vehicle seat includes aseat element mounted to a vehicle structure and a seat support memberfor supporting a seat bottom. A plurality of weight sensor assembliesare mounted between the seat element and the seat support member. Eachof the weight sensor assemblies has a bottom surface and a top surfacewith a full bridge strain gage mounted on one of the surfaces.

[0010] In a preferred embodiment, each weight sensor assembly has afirst end mounted to the seat element, such as a seat riser, and asecond end mounted to the seat support member, such as a seat frame ortrack member, with a central bendable portion extending between thefirst and second ends. The strain gages each generate a weight signal inresponse to measuring deflection of the central bendable portion for therespective sensor assembly. A central processor determines the seatoccupant weight based on the weight signals. An airbag control modulecommunicates with the processor to control deployment force of an airbagbased on seat occupant weight.

[0011] In a further preferred embodiment, each of the sensors includesat least one groove formed in one of the top or bottom surfaces. Thegroove extends at least partially along the width of the sensor tolocalize strain in the central bendable portion. The strain gage isplaced on the other of the top or bottom surfaces, facing opposite fromthe groove.

[0012] The subject invention provides a simplified seat occupant weightmeasurement system that is inexpensive, accurate, and easily to install.These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an environmental view of a seat occupant seated in avehicle having an airbag system.

[0014]FIG. 2 is an exploded view of a seat assembly incorporating thesubject weight measurement system.

[0015]FIG. 3 is a side view, partially cut-away, of the seat of FIG. 2showing the mounting of one sensor assembly.

[0016]FIG. 4 is a perspective view of the sensor assembly of FIG. 3.

[0017]FIG. 5 is a schematic diagram of the control system incorporatingthe subject weight measurement system.

[0018]FIG. 6A is a top perspective view of a preferred embodiment of asensor assembly.

[0019]FIG. 6B is a bottom perspective view of the sensor assembly ofFIG. 6A.

[0020]FIG. 6C is a cross-section view of the sensor assembly taken along6C-6C of FIG. 6A.

[0021]FIG. 7 is an alternate embodiment of a weight sensor.

[0022]FIG. 8 is an alternate embodiment of a weight sensor.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

[0023] A vehicle includes a vehicle seat assembly, shown generally at 12in FIG. 1, and an airbag system 14. The seat assembly 12 can be either adriver or passenger seat and includes a seat back 16 and a seat bottom18. When a vehicle occupant 20 is seated on the seat 12 a vertical forceFv is exerted against the seat bottom 18. The vertical force Fvrepresents the weight of the seat occupant 20.

[0024] The airbag system 14 deploys an airbag 24 under certain collisionconditions. The deployment force for the airbag 24, shown in dashedlines in FIG. 1, varies according to the weight of the occupant 20. Thevehicle includes a unique system for measuring the weight of the seatoccupant 20. This unique system is integrated into a seat frame or trackmember, generally indicated at 26 in FIG. 2.

[0025] The seat 12 is preferably mounted to a vehicle structure 30 on aninboard track assembly 26 a and an outboard track assembly 26 b that isspaced apart from the inboard track assembly 26 a by a predetermineddistance. Both the inboard 26 a and outboard 26 b track assembliesinclude first 28 and second 32 track members. The first track member 28is typically mounted to a seat riser 34 or directly to the vehiclestructure 30, such as a floor. The second track member 32 is mounted forsliding movement relative to the first track member 28 so that seat 12position can be adjusted forwardly and rearwardly within the vehicle toa desired position.

[0026] A plurality of sensor assemblies 36 are mounted between the firsttrack members 28 of the inboard 26 a and outboard 26 b track assembliesand the riser 34. In the preferred embodiment, four (4) sensorassemblies 36 are used with a first sensor assembly 36 a positioned nearthe front of the inboard track assembly 26 a, a second sensor assembly36 b positioned near the rear of the inboard track assembly 26 a, athird sensor assembly 36 c positioned near the front of the outboardtrack assembly 26 b, and a fourth sensor assembly 36 d positioned nearthe rear of the outboard track assembly 26 b.

[0027] Preferably, each sensor assembly 36 a, 36 b, 36 c, and 36 d has afirst end 40 mounted to the first track member 28 with at least onefastener 42 and a second end 44 mounted to the riser 34 with at leastone fastener 42, as shown in FIG. 3. It should be understood that anytype of fastener can be used and that other joining methods known in theart can also be used to mount the sensors 36. A central bendable portion46 extends between the first 40 and second 44 ends of the sensorassembly 36. As the vertical force Fv of the seat occupant 20 is exertedon the seat bottom 18, the central bendable portion 46 of each sensorassembly 36 a, 36 b, 36 c, 36 d deflects or bends into an S-shapedconfiguration putting one portion of the sensor 36 in compression andanother portion in tension.

[0028] In the embodiment of FIGS. 3 and 4, the first 40 and second 44ends are raised above/below the central bendable portion 46 to formsteps 38 on each side of the central bendable portion 46. The height ofthe steps 38 can be varied. This configuration forms gaps between thesensor 36 and the track member 28 and between the sensor 36 and theriser 34 to facilitate bending.

[0029] A strain gage 50 is mounted to each of the sensors 36 a, 36 b, 36c, 36 d to measure the amount of bending in the central portion 46. Thesensors 36 have a top surface 52 facing the seat bottom 18 and a bottomsurface 54 facing the riser 34. Preferably, a combination of four (4)strain gages, forming a full bridge, are mounted on one of the top 52 orbottom 54 surfaces to measure the bending. The four strain gages arethus combined to serve as a Wheatstone Bridge for measuring deflection.The operation of a Wheatstone Bridge is well known in the art.

[0030] As shown in FIG. 4, the stain gage 50 is mounted on the topsurface 52 of the sensor 36. A first aperture 56 is formed at the firstend 40 of the sensor 36 and a second aperture 58 is formed at the secondend 44 of the sensor 36 for receiving the fasteners 42. The strain gage50 is positioned between the apertures 56, 58 on the top surface 52. Inorder to achieve more accurate readings, full-bridge strain gage 50should have all strain gage components mounted on only one surface ofthe sensor 36. In other words, if the strain gage 50 is mounted on thetop surface 52 then no strain gage components should be mounted on thebottom surface 54 or if the gage 50 is mounted on the bottom surface 54then no strain gage components should be mounted on the top surface 52.

[0031] The sensors 36 a, 36 b, 36 c, 36 d each generate a signalrepresentative of the occupant weight that causes bending at therespective location of the sensors 36 a, 36 b, 36 c, 36 d, see FIG. 5.Thus, the first sensor 36 a generates a first signal 60, the secondsensor 36 b generates a second signal 62, the third sensor 36 cgenerates a third signal 64, and the fourth sensor 36 d generates afourth signal 66. The signals 60, 62, 64, 66 are transmitted to a commoninterface unit 68 and are then fed into a central processor unit orelectronic control unit (ECU) 70 as is known in the art. The ECU 70combines the signals 60, 62, 64, 66 to determine the weight of theoccupant 20. The ECU 70 then sends a control signal 72 to a systemcontroller 74. Preferably, the system controller 74 is an airbag controlmodule that is in communication with the ECU 70 such that the deploymentforce of the airbag 24 is controlled based on seat occupant weight. Thesystem controller 70 could also be used to control the force of seatbelt pretensioners based on occupant weight. A vehicle crash sensor 76also supplies information to the airbag control module 74 that is usedin preparation for the control instructions for the airbag 24. Thesystem utilizes a power supply 78 as is known in the art.

[0032] A preferred embodiment of a weight sensor 136 is shown in FIGS.6A-6C. In this preferred embodiment each of the sensor assemblies 136 a,136 b, 136 c, 136 d includes at least one groove 80 formed in one of thetop 52 or bottom 54 surfaces of the sensor 36. The groove 80 extends atleast partially along the width of the sensor assembly 36 to localizestrain in the central bendable portion 46. The full bridge strain gage50 is placed the opposing surface, facing an opposite direction from thegroove 80, see FIG. 6B. In this embodiment, the groove 80 extends acrossthe entire with of the sensor 36.

[0033] In an alternate embodiment of a weight sensor 236, shown in FIG.7, a pair of grooves 80 a, 80 b are formed in one of the top 52 orbottom 54 surfaces to localize strain in the central bendable portion46. The grooves 80 a, 80 b are spaced apart from one another and onlyextend partially across the width of the sensor 36. In this embodiment,the strain gage 50 is mounted between the grooves 80 a, 80 b.

[0034] In another alternate embodiment of a weight sensor 336, shown inFIG. 8, the sensor assembly 36 has a generally flat central bendableportion 46. A notch 84 is formed at one end that separates a pair ofholes 86 that are used to connect the sensor 36 to the interface 68.

[0035] The subject invention offers a simplified system for measuringthe weight of a seat occupant 20. It is preferable to integrate thesensors 36 between the track 28 and the riser 34 because they are commoncomponents for most vehicle seats 12. The subject weight measurementsystem is easily incorporated into any type of seat configuration. Themeasured weight is independent of seat position and is accuratelyprovided in various occupant positions on the seat 12.

[0036] By measuring the deflection in all four (4) locations in theinboard 26 a and outboard 26 b track assemblies, it is possible tocalculate the occupant weight, which is proportional to the sum of theoutput of all of the sensors 36 a, 36 b, 36 c, 36 d. The electronics forsignal conditioning and the interface 68 can be housed within the trackassemblies 26 a, 26 b as is well known in the art.

[0037] Although a preferred embodiment of this invention has beendisclosed, it should be understood that a worker of ordinary skill inthe art would recognize many modifications come within the scope of thisinvention. For that reason, the following claims should be studied todetermine the true scope and content of this invention.

I claim:
 1. A system for measuring the weight of an occupant seated on a vehicle seat comprising: a seat element mounted to a vehicle structure; a seat support member for supporting a seat bottom; and a plurality of weight sensor assemblies mounted between said seat element and said seat support member, each of said weight sensor assemblies having a bottom surface and a top surface with a full bridge strain gage mounted on one of said surfaces.
 2. A system according to claim 1 wherein said full bridge strain gage is mounted to said bottom surface.
 3. A system according to claim 1 wherein said seat element includes a seat riser that is mounted to a vehicle floor.
 4. A system according to claim 3 wherein said seat support member is a seat track member fixed to said riser.
 5. A system according to claim 4 wherein each of said sensor assemblies has a first end fixed to said seat track and a second end fixed to said riser with a central bendable portion extending between said first and second ends.
 6. A system according to claim 5 wherein said full bridge strain gage is mounted on said central bendable portion.
 7. A system according to claim 1 wherein each of said sensor assemblies includes a central bendable portion with at least one groove formed in one of said top or bottom surfaces and extending at least partially along the width of said sensor assembly to localize strain in said central bendable portion.
 8. A system according to claim 7 wherein said full bridge strain gage is placed on the other of said top or bottom surfaces, facing opposite from said groove.
 9. A system according to claim 1 wherein each of said sensor assemblies generates a weight signal representing a portion of the weight of a seat occupant that is transmitted to a central processing unit to determine seat occupant weight.
 10. A system according to claim 9 including an airbag control module in communication with said processor wherein deployment force of an airbag is controlled by said control module based on seat occupant weight.
 11. A system for measuring the weight of an occupant seated on a vehicle seat comprising: a seat riser mounted to a vehicle structure; a seat frame member for supporting a seat bottom; a plurality of weight sensors each having a first end mounted to said seat riser and a second end mounted to said seat frame with a central bendable portion extending between said first and second ends; a strain gage assembly mounted only on either a top or bottom surface of each of said weight sensors for generating a weight signal in response to measuring deflection of said central bendable portion; a central processor for determining seat occupant weight based on said weight signals; and an airbag control module in communication with said processor wherein deployment force of an airbag is controlled by said control module based on seat occupant weight.
 12. A system according to claim 11 wherein each of said sensors includes at least one groove formed in one of said top or bottom surfaces and extending at least partially along the width of said sensor to localize strain in said central bendable portion.
 13. A system according to claim 12 wherein said strain gage assembly is placed on the other of said top or bottom surfaces, facing opposite from said groove.
 14. A system according to claim 13 wherein said each of said strain gage assemblies is a full bridge gage.
 15. A system according to claim 14 wherein each of said full bridge gages are mounted on said bottom surface of said sensors.
 16. A system for measuring the weight of an occupant seated on a vehicle seat comprising: a seat bottom; an inboard track assembly and an outboard track assembly spaced apart from each other and mounted to the vehicle structure, said inboard and outboard track assemblies each having a first track mounted to a seat riser and an second track mounted for movement relative to said first track; a first weight sensor positioned near a forward portion of said inboard track assembly; a second weight sensor positioned near a rearward portion of said inboard track assembly; a third weight sensor positioned near a forward portion of said outboard track assembly; a fourth weight sensor positioned near a rearward portion of said outboard track assembly; each of said weight sensors having a first end fixed to said first track and a second end fixed to said riser with a central bendable portion extending between said first and second ends; at least one groove formed in one of a top or bottom surface of each of said sensors and extending at least partially along the width of said sensor to localize strain in said central bendable portion; a full bridge strain gage assembly mounted on the other of said top or bottom surfaces of each of said sensors, facing away from said groove, said gage assemblies each generating a weight signal in response to measuring deflection of said central bendable portion of said respective sensor; a central processor for determining seat occupant weight based on said weight signals; and an airbag control module in communication with said processor wherein deployment force of an airbag is controlled by said control module based on seat occupant weight. 